Reforming a sulfur-free gasoline fraction with a platinum-germanium catalyst

ABSTRACT

A substantially sulfur-free gasoline fraction is catalytically reformed by contacting it and a substantially sulfur-free hydrogen stream with a substantially sulfur-free, bimetallic catalyst comprising a combination of a platinum group component, a germanium component and a halogen component with a porous carrier material, at reforming conditions. Key features of the disclosed process are: (1) use of substantially sulfur-free charge stock and hydrogen stream; (2) maintenance of substantially all of the platinum group component of the bimetallic catalyst in the elemental state; (3) presence of substantially all of the germanium component of the bimetallic catalyst in an oxidation state above that of the elemental metal, and (4) maintenance of the bimetallic catalyst in a substantially sulfur-free state during the processing period.

United States Patentv [1 1 Hayes [54] REFORMING A SULFUR-FREE GASOLINE FRACTION WITH A PLATINUM-GERMANIUM CATALYST John C. Hayes, Palatine, Ill.

[73] Assignee: Universal Oil Products Company, Des Plaines, Ill.

[22] Filed: May 10, 1971 [21] Appl. No.: 141,980

Related US. Application Data [63] Continuation-impart of Ser. Nos. 828,762, May 28, 1969, Pat. No. 3,578,584, and Ser. No. 876,077, Nov. 12, 1969, abandoned.

[75] Inventor:

11] 3,748,260 5] July 24, 1973 3,565,789 2/1971 Lovell 208/138 Primary Examiner-Herbert Levine AttorneyJames R. Hoatson, Jr. and Thomas K.

McBride [57] ABSTRACT A substantially sulfur-free gasoline fraction is catalytically reformed by contacting it and a substantially sulfur-free hydrogen stream with a substantially sulfurfree, bimetallic catalyst comprising a combination of a platinum group component, a germanium component and a halogen component with a porous carrier material, at reforming conditions. Key features of the disclosed process are: (1) use of substantially sulfur-free charge stock and hydrogen stream; (2) maintenance of substantially all of the platinum group component of the bimetallic catalyst in the elemental state; (3) presence of substantially all of the germanium component of the bimetallic catalyst in an oxidation state above that of the elemental metal, and (4) maintenance of the bimetallic catalyst in a substantially sulfur-free state during the processing period.

10 Claims, No Drawings REFORMING A SULFUR-FREE GASOLINE FRACTION WITH A PLATINUM-GERMANIUM CATALYST CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of my prior, copending application Ser. No. 828,762, now US. Pat. No. 3,578,584, which was filed on May 28, 1969, and of my prior, copending application Ser. No. 876,077, which was filed on Nov. 12, 1969 and now abandoned.

The subject of the present invention is an improved catalytic reforming process wherein a unique bimetallic catalyst is coupled with the use of a substantially sulfurfree environment to enable a substantial increase in the activity, selectivity and stability characteristics of the resulting process. More precisely, the present invention involves the use of a novel bimetallic catalyst in a reforming process which is operated in a substantially sulfur-free environment, thereby preventing detrimental interaction of sulfur with this bimetallic catalyst and allowing the catalyst to perform in a more efficient and effective manner. In one important aspect, the present invention involves the use of a substantially sulfur-free, bimetallic catalytic composite comprising a combination of a platinum group component, a germanium component and a halogen component with a porous carrier material (the catalyst having substantially all of the platinum group compound present as elemental metal and substantially all of the germanium component present in an oxidation state above that of the elemental metal) in a reforming process which is maintained substantially free of sulfur and sulfur-containing compounds by catalytically pretreating the feed to remove substantially all sulfurous contaminants therefrom. In another aspect, this type of bimetallic catalyst is utilized in a catalytic reforming process which is not only maintained free of sulfur but also is carefully controlled so that the amount of water and waterproducing substances entering therein is held to a low level.

Composites having a hydrogenationdehydrogenation function and a cracking function are widely used today as catalysts in many industries, such as the petroleum and petrochemical industry, to accelerate a wide spectrum of hydrocarbon conversion reactions. Generally, the cracking function is thought to be associated with an acid-acting material of the porous, adsorptive, refractory oxide type which is typically utilized as the support or carrier for a heavy metal component such as the metals or compounds of metals of groups V through VIII of the Periodic Table to which are generally attributed the hydrogenationdehydrogenation function.

These catalytic composites are used to accelerate a wide variety of hydrocarbon conversion reactions .such as hydrocracking, isomerization, dehydrogenation, hydrogenation, desulfurization, cyclization, alkylation, polymerization, cracking, hydroisomerization, etc. In many cases, the commercial applications of these catalysts are in processes where more than one of these reactions are proceeding simultaneously. An example of this type of process is reforming wherein a hydrocarbon feed stream .containing paraffins and naphthenes is subjected to conditions which promote dehydrogenation of naphthenes to aromatics, dehydrocyclization of paraffins to aromatics, isomerization of paraffins and naphthenes, hydrocracking of naphthenes and paraffins and the like reactions to produce an octane-rich or aromatic-rich product stream. Another example is a hydrocracking process wherein catalysts of this type are utilized to effect selective hydrogenation and cracking of high molecular weight unsaturated materials, selective hydrocracking of high molecular weight materials, and other like reactions, to produce a generally lower boiling, more valuable output stream. Yet another example is an isomerization process wherein a hydrocarbon fraction which is relatively rich in straight-chain paraffin components is contacted with a dual-function catalyst to produce an output stream rich in isoparaffin compounds.

Regardless of the reaction involved or the particular process involved, it is of critical importance that the dual-function catalyst exhibit not only the capability to initiate perform its specified functions, but also that it has the capability to perform them satisfactorily for prolonged periods of time. The analytical terms used in the art to measure how well a particular catalyst performs its intended functions in a particular hydrocarbon reaction environment are activity, selectivity, and stability. And for purposes of discussion here, these terms are conveniently defined for a given charge stock as follows: (1) activity is a measure of the catalysts ability to convert hydrocarbon reactants into products at a specified severity level where severity level means the conditions used that is, the temperature, pressure, contact time, and'presence of diluents such as H (2) selectivity refers to the amount of desired product or products obtained relative to the amount of reactants converted or charged; (3) stability refers to the rate of change with time of the activity and selectivity parameters obviously the smaller rate implying the more stable catalyst. In a reforming process, for'example, activity commonly refers to the amount of conversion that takes place for a given charge stock at a specified severity level and is typically measured by octane number of the C product stream; selectivity usually refers to the relative amount of C yield that is obtained at the particular severity level; and stability is typically equated to the rate of change with time of activity, as measured by octane number of C product and of selectivity, as measured by C yield. Actually, the last statement is not strictly correct because generally a continuous reforming process is run to produce a constant octane C product witha severity level being continuously adjusted to attain this result; and, furthermore, the severity level is for this process usually varied by adjusting the conversion temperature in the reaction zone so that in point of fact, the rate of change of activity finds response in the rate of change of conversion temperatures and changes in this last parameter are customarily taken as indicative of activity stability.

As is well known to those skilled in the art, the principal cause of observed deactivation or instability of a dual-function catalyst when it is used in a hydrocarbon conversion reaction is associated with the fact that coke forms on the surface of the catalyst during the course of the reaction. More specifically, in these hydrocarbon conversion processes, the conditions utilized typically result in the formation of heavy, high molecular weight, black, solid or semi-solid, carbonaceous material which coats the surface of the catalyst and reduces its activity by shielding its active sites from the reactants. In other words, the performance of this dual-function catalyst is sensitive to the presence of carbonaceous deposits on the surface of the catalyst. Accordingly, the major problem facing workers in this area of the art is the development of more active and selective catalytic composites that are not as sensitive to the presence of these carbonaceous materials and/or have the capability to suppress the rate of the formation of these carbonaceous materials on the catalyst. Viewed in terms of performance parameters, the problem is to develop a dual-function catalyst having superior activity, selectivity, and stability. In particular, for a reforming process the problem is typically expressed in terms of shifting and stabilizing the C yield-octane relationship C yield being representative of selectivity, and octane being proportional to activity.

In my prior applications, I disclosed a dual-function bimetallic catalytic composite which possesses improved activity, selectivity, and stability when it is employed in a process for the conversion of hydrocarbons of the type which have heretofore utilized dualfunction catalytic composites such as processes for isomerization, hydroisomerization, dehydrogenation, desulfurization, denitrogenization, hydrogenation, alkylation, dealkylation, disproportionation, oligomerization, hydrodealkylation, transalkylation, cyclization, dehydrocyclization, cracking, hydrocracking, reforming, and the like processes. In particular, I reported on my discovery that the use of a bimetallic catalyst, comprising a combination of a platinum group component, a germanium component, and a halogen component with a porous refractory carrier material, can enable the performance of a hydrocarbon conversion process utilizing a dual-function catalyst to be substantially improved.

I have previously established that an essential condition associated with the acquisition of this improved performance of this bimetallic catalyst is the oxidation state of the germanium component utilized in this catalyst. My findings here were that the germanium component must be utilized in a positive oxidation state (i.e., either +2 or +4) and that the germanium component must be uniformly distributed throughout the porous carrier material. In addition, I found that in order to achieve the desired oxidation state and the distribution of the germanium component, the presence of a halogen component ip the composite was essential. Furthermore, l disclosed that the catalyst must be prepared under carefully controlled conditions in order to achieve the desired oxidation state as will be explained hereinafter. In the case of a reforming process, one of the principal advantages associated with the use of this bimetallic catalyst was that it enabled the reforming process to operate in a highly stable manner in a highseverity operation; for example, a continuous reforming process producing a C reformate having an octane of about I00 F-l clear and utilizing a relatively low pressure selected from the range of about 50 to about 350 psig. In short, the invention disclosed in my prior applications essentially involves the finding that the addition of a controlled amount of an oxidized germanium component to a dual-function hydrocarbon conversion catalyst containing a platinum group component and a halogen component enabled the performance characteristics of the catalyst to be sharply and materially improved.

According to the present invention, 1 have now discerned that a further improvement in a reforming process using the type of bimetallic catalyst described above is possible if the reforming zone is maintained substantially free of sulfur. By the use of the expression substantially free of sulfur it is intended to cover the situation where the reforming zone or the environment containing the catalyst is maintained substantially free of sulfur and sulfur-containing compounds particularly, free of sulfide and of sulfur-containing compounds that yield hydrogen sulfide at catalytic reforming conditions. The concept of the present invention developed from a series of experiments which I performed in order to investigate the sulfur sensitivity of this type of bimetallic catalyst. As a result of these experiments, I have now ascertained that this type of bimetallic catalyst is extremely sensitive to the presence of sulfur in its environment regardless of the atomic ratio of the metallic ingredients contained therein. In particular, I have observed that the presence of sulfur in the charge stock can cause the performance of this catalyst in a catalytic reforming process to decay at an accelerated rate relative to the performance observed in the absence of sulfur. In short, the present invention especially involves the finding that this particular type of bimetallic catalyst performs in the superior manner in a catalytic reforming process if sulfur is excluded therefrom.

It is accordingly an object of the present invention to provide an improved method of operating a catalytic reforming process which utilizes a bimetallic catalyst of the type described herein.

In one embodiment, the present invention is a process for catalytically reforming a substantially sulfurfree gasoline fraction with a substantially sulfur-free bimetallic catalyst comprising a combination of a platinum group component, a germanium component and a halogen component with a porous carrier material. According to this process, the gasoline fraction and a substantially sulfur-free hydrogen stream are contacted with the bimetallic catalyst at reforming conditions. The bimetallic catalyst is characterized by the states in which the metallic components are present therein; specifically, substantially all of the platinum group component is present as the elemental metal and substantially all of the germanium component is present in an oxidation state abovethe elemental metal. Moreover, this catalyst is maintained throughout the processing period in a substantially sulfur-free state by excluding sulfur from the gasoline fraction and hydrogen stream charged to the process. Additionally, the bimetallic catalyst contains these components in amounts sufficient to result in a composite containing, on an elemental basis, about 0.1 to about 2 wt. percent of the platinum metal, about 0.0l to about 5-wt-. percent of germanium and about 0.5 to about 3.5 wt. percent halogen.

In another embodiment, the present invention relates to an improvement in a catalytic reforming process wherein a sulfur-containing gasoline charge stack and autogenous hydrogen are contacted with a bimetallic catalyst at reforming conditions. The bimetallic catalyst comprises a combination of a platinum group metal, a germanium component, and a halogen component with a porous carrier material in a manner such that substantially all of the platinum group component is present as the elemental metal and substantially all of the germanium component is present in an oxidation state above that of the elemental metal and such that the catalyst contains, on an elemental basis, about 0.01 to about 2 wt. percent platinum, about 0.01 to about 5 wt. percent germanium and about 0.5 to about 3.5 wt. percent halogen. Against this background, the improvement of the present invention involves pretreating the gasoline charge stock to this process in order to remove substantially all of the sulfurous nitrogenous and water-yielding contaminants.

Other objects and embodiments of the present invention encompass further details about preferred ingredients and amounts of ingredients for this special kind of bimetallic catalyst, methods of preparing this catalyst, types of charge stocks that can be catalytically reformed in the present process, and conditions and procedures for performing the instant improved process. These are all hereinafter presented in the following detailed discussion of each of these facets of the present invention.

The bimetallic catalyst utilized in the present invention comprises a porous carrier material or support having combined therewith a platinum group component, a germanium component, and a halogen component. Considering first the porous carrier material, it is preferred that the material be a porous, adsorptive, high-surface area support having a surface area of about 25 to about 500 m lg. The porous carrier material should be relatively refractory to the conditions utilized in the hydrocarbon conversion process, and it is intended to include carrier materials which have traditionally been utilized in dual-function hydrocarbon conversion catalysts such as: (1) activated carbon, coke, or charcoal; (2) silica or silica gel, clays and silicates including those synthetically prepared and naturally occurring, which may or may not be acid treated, for example, attapulgus clay, china clay, diatomaceous earth, fullers earth, kaolin, kieselguhr, pumice, etc.; (3) ceramics, porcelain, crushed firebrick, and bauxite; (4) refractory inorganic oxides such as alumina, titanium dioxide, zirconium dioxide, chromium oxide, zinc oxide, magnesia, thoria, boria, silica-alumina, silicamagnesia, chromia-alumina, alumina-boria, silicazirconia, etc.; (5) crystalline aluminosilicates such as naturally occurring or synthetically prepared mordenite and/or faujasite, either in the hydrogen form or in a form which has been treated with multi-valent cations; and, (6) combinations of one or more elements from one or more of these groups. The preferred porous carrier materials are refractory inorganic oxides, with best results obtained with an alumina carrier material. Suitable alumina materials are the crystalline aluminas known as the gamma, eta-, and theta-aluminas, with gammaor eta-alumina giving best results. In addition, in some embodiments the alumina carrier material may contain minor proportions of other well known refractory inorganic oxides such as silica, zirconia, magnesia, etc.; however, the preferred carrier material is substantially pure gammaor eta-alumina. Preferred carrier materials have an apparent bulk density of about 0.3 to about 0.7 g/cc and surface area characteristics such that the average pore diameter is about to 300 Angstroms, the pore volume is about 0.1 to about 1 ml/g and the surface area is about 100 to about 500 m /g. In general, best results are typically obtained with a gamma-alumina carrier material which is used in the form of spherical particles having: a relatively small diameter (i.e., typically about 1/16 inch), an apparent bulk density of about 0.5 g/cc, a pore volume of about 0.4 ml/g, and a surface area of about m /g.

The preferred alumina carrier material may be prepared in any suitable manner and may be synthetically prepared or natural occurring. Whatever type of alumina is employed it may be activated prior to use by one or more treatments including drying, calcination, steaming, etc., and it may be in a form known as activated alumina, activated alumina of commerce, porous alumina, alumina gel, etc. For example, the alumina carrier may be prepared by adding a suitable alkaline reagent, such as ammonium hydroxide, to a salt of aluminum such as aluminum chloride, aluminum nitrate, etc., in an amount to form an aluminum hydroxide gel which upon drying and calcining is converted to alumina. The alumina may be formed in any desired shape such as spheres, pills, cakes, extrudates, powders, granules, etc., and utilized in any desired size. For the purpose of the present invention, a particularly preferred form of alumina is the sphere; and alumina spheres may be continuously manufactured by the well known oil drop method which comprises: forming an alumina hydrosol by any of the techniques taught in the art and preferably by reacting aluminum metal with hydrochloric acid, combining the hydrosol with a suitable gelling agent and dropping the resultant mixture into an oil bath maintained at elevated temperatures. The droplets of the mixture remain in the oil bath until they set and form hydrogel spheres. The spheres are then continuously withdrawn from the oil bath and typically subjected to specific aging treatments in oil and an ammoniacal solution to further improve their physical characteristics. The resulting aged and gelled particles are then washed and dried at a relatively low temperature of about 300 F. to about 400 F. and subjected to a calcination procedure at a temperature of about 850 F. to about 1300 F. for a period of about 1 to about 20 hours. This treatment effects conversion of the alumina hydrogel to the corresponding crystalline gammaalumina. See the teachings of U. S. Pat. No. 2,620,314 for additional details.

One essential constituent of the bimetallic catalyst used in the present process is a germanium component. It is an essential feature of the type of bimetallic catalyst of interest here that substantially all of the germanium component is present in the composite in an oxidation state above that of the elemental metal. That is, the germanium component must exist in the catalytic composite in either the +2 or +4 oxidation state, with the latter being the most likely state. Accordingly, the germanium component can be present in the composite as a chemical compound, such as the oxide, sulfide, halide, etc., wherein the germanium is in the required oxidation state, or as a chemical combination with the carrier material in which combination the germanium ex ists in this higher oxidation state. On the basis of the evidence currently available, it is believed that the germanium component in the subject composite exists as germanous or germanic oxide. lt is important to note that this limitation on the state of the germanium component requires extreme care in the preparation and use of the subject composite in order to insure that it is not subjected to high temperature reduction conditions effective to produce the germanium metal. This germanium component may be incorporated in the catalytic composite in any suitable manner known to the art such as by coprecipitation or cogellation with the porous carrier material, ion exchange with the gelled carrier material or impregnation with the carrier material either after or before it is dried and calcined. On method of incorporating the germanium component into the catalytic composite involves coprecipitating the germanium component during the preparation of the preferred carrier material, alumina. This method typically involves the addition of a suitable soluble decomposable germanium compound such as germanium tetrachloride to the alumina hydrosol and then combining the hydrosol with a suitable gelling agent and dropping the resulting mixture into an oil bath, etc., as explained in detail hereinbefore. After drying and oxidizing the resulting gelled carrier material there is obtained an intimate combination of alumina and germanium oxide. A preferred method of incorporating the germanium component into the catalytic composite involves utilization of a soluble, decomposable compound of germanium to impregnate the porous carrier material. In general, the solvent used in this impregnation step is selected on the basis of the capability to dissolve the desired germanium compound, and it'is preferably an aqueous, acidic solution. Thus, the germanium component may be added to the carrier material by commingling the latter with an aqueous, acidic solution of suitable germanium salt or suitable compound of germanium such as germanium dioxide, germanium tetrachloride, germanium difluoride, germanium tetrafluoride, germanium di-iodide, germanium monosul fide, and the like compounds. Particularly preferred impregnation solutions comprise germanium dissolved in chlorine water or germanium tetrachloride dissolved in anhydrous alcohol. In general, the germanium component can be impregnated either prior to, simultaneously with or after the platinum group component is added to the carrier material. Excellent results are obtained when the germanium component is impregnated simultaneously with the platinum group component. In fact, a preferred impregnation solution contains chloroplatinic acid, hydrogen chloride, and germanium dissolved in chlorine water.

Regardless of which germanium compound is used in the preferred impregnation step, it is important that the germanium component be uniformly distributed throughout the carrier material. In order to achieve this objective it is necessary to maintain the pH of the impregnation solution in a range of about 1 to about 7 and to dilute the impregnation solution to a volume which is substantially in excess of the volume of the carrier material which is impregnated. It is preferred to use a volume ratio of impregnation solution to carrier material of at least 1.5:] and preferably about 2:1 to about 10:1 or more. Similarly, it is preferred to use a relatively long contact time during the impregnation step ranging from about 54 hour up to about hour or more before drying to remove excess solvent in order to insure a high dispersion of the germanium component on the carrier material. The carrier material is, likewise, preferably constantly agitated during this preferred impregnation step.

The bimetallic catalyst used in the present invention also contains a platinum group component. Although the process of the present invention is specifically directed to the use of a catalytic composite containing platinum, it is intended to include other platinum group metals such as palladium, rhodium, ruthenium, os-

mium, and iridium. An essential feature of the instant bimetallic catalyst is that substantially all of the platinum group component, such as platinum, exists in the final catalytic composite in the elemental state. This state is achieved by the hereinafter described reduction step which is designed to reduce substantially all of this component to the elemental metal without reducing the germanium component; Generally, the amount of the platinum group component present in the final catalyst composite is small compared to the quantities of the other components combined therewith. In fact, the platinum group component generally comprises about 0.01 to about 2 wt. percent of the final catalytic com posite, calculated on an elemental basis. Excellent results are obtained when the catalyst contains about 0.05 to about 1 wt. percent of the platinum group metal. The preferred platinum group component is ele mental platinum metal. I

The platinum group component may be incorporated in the catalytic composite in any suitable manner such as coprecipitation or cogellation with the preferred carrier material, or ion exchange or impregnation thereof. The preferred method of preparing the catalyst involves the utilization of a water-soluble, decomposable compound of a platinum group metal to impregnate the carrier material. Thus, the platinum group component may be added to the support by commingling the latter with an aqueous solution of chloroplatinic acid. Other water-soluble compounds of platinum group metals may be employed in impregnation solutions and include ammonium chloroplatinate, bromoplatinic acid, platinum dichloride, platinum tetrachloride hydrate, platinum dichlorocarbonyl dichloride, dinitro diaminoplatinum, palladium chloride, palladium nitrate, chloropalladic acid, etc. The utilization of a platinum group metal chloride compound, such as chloroplatinic acid, is preferred since it facilitates the incorporation of both the platinum group component and at least a minor quantity of the halogen component in a single step. Hydrogen chloride or the like acid is also generally added to the impregnation solution in order to further facilitate the incorporation of the halogen component and to aid in the distribution of the metallic components throughout the carrier material. In addition, it is generally preferred to impregnate the carrier material after it has been calcined in order to minimize the risk of washing away the valuable platinum metal compounds; however, in some cases it may be advantageous to impregnate the carrier material when it is in a gelled state.

Another essential constituent of the bimetallic catalyst is the halogen component. Although the precise form of the chemistry of the association of the halogen component with the carrier material is not entirely known, it is customary in the art to refer to the halogen component as being combined with the carrier material or with the other ingredients of the catalyst. This combined halogen may be either fluorine, chlorine, iodine, bromine, or mixtures thereof. Of these, fluorine and, particularly, chlorine are preferred. The halogen may be added to the carrier material in any suitable manner either during preparation of the carrier material or before or after the addition of the other components. For example, the halogen may be added at any stage of the preparation of the carrier material or to the calcined carrier material as an aqueous solution of a watersoluble decomposable halogen-containing compound such as hydrogen fluoride, hydrogen chloride, hydrogen bromide, ammonium chloride, etc. The halogen component or a portion thereof may be composited with the carrier material during the impregnation of the latter with the platinum group component; for example, through the utilization of a mixture of chloroplatinic acid and hydrogen chloride. In another situation, the alumina hydrosol which is typically utilized to form the preferred alumina carrier material may contain halogen and thus contribute at least a portion of the halogen component to the final composite. For reforming, the halogen is combined with the carrier material in an amount sufficient to result in a final composite that contains about 0.5 to about 3.5 wt. percent and preferably about 0.6 to about 1.2 percent by weight of the halogen, calculated on an elemental basis. The preferred halogen component is chlorine or a compound thereof.

The halogen component is utilized in the bimetallic catalyst for two purposes: one involves the traditional enhancement of the acidic function of the resulting composite, the other involves the achievement and maintenance of a uniform distribution of the oxidized germanium component in the carrier material. I have observed that a high dispersion of small crystallites of the germanium component in the carrier material is essential for the maintenance of the germanium component in an oxidized state under the reduction conditions used in the hereinafter described reduction step as well as the reduction conditions encountered in the use of the composite in, for example, a reforming process. One of the principal effects of incorporating the halogen component in the composite is that it acts to hold or fix the germanium component in a highly dispersed state where it is highly resistant to the subsequent reduction conditions. Despite this resistance, it is still necessary to carefully control the conditions to which the composite is subjected in order to insure that the germanium is maintained in an oxidized state; that is to say, prolonged exposure of the composite to hydrogen at temperatures substantially above about 1000" F. are to be avoided.

Relative to the amount of the germanium component contained in the bimetallic catalyst, it is preferably sufficient to constitute about 0.01 to about wt. percent of the final composite, calculated on an elemental basis, although substantially higher amounts of germanium may be utilized in some cases. Best results are typically obtained with about 0.05 to about 2 wt. percent germanium. In the case where the germanium component is incorporated in the catalyst by coprecipitating it with the preferred alumina carrier material, it is within the scope of the present invention to prepare composites containing up to 30 wt. percent germanium, calculated on an elemental basis. Regardless of the absolute amounts of the germanium component and the platinum group component utilized, the atomic ratio of germanium to the platinum group metal contained in the catalyst is preferably selected from the range of about 0.3:] to about 10:1 with best results achieved at an atomic ratio of about 0.6:1 to 6:1. This is particularly true when the total content of the germanium component plus the platinum group component in the catalytic composite is fixed in the range of about 0.1 to about 3 wt. percent thereof, calculated on an elemental germanium and platinum group metal basis.

Regardless of the details of how the components are combined with the porous carrier material, the final bimetallic catalyst generally will be dried at a temperature of about 200 to about 600 F. for a period of at least about 1 to about 24 hours or more, and finally oxidized or calcined at a temperature of about 700 F. to about l F. in an air atmosphere for a period of at least about 0.5 to about 10 hours in order to convert the metallic components substantially to the oxide form. Best results are generally obtained when the halogen content of the catalyst is adjusted during this oxidation step by including a halogen or a halogencontaining compound in the air atmosphere utilized. In particular, when the halogen component of the catalyst is chlorine, it is preferred to use a mole ratio of H 0 to HCl of about 20:1 to about 100:] during at least a portion of the oxidation step in order to adjust the final chlorine content of the catalyst to a range of about 0.6 to about 1.2 wt. percent.

It is essential that the resultant calcined catalytic composite be subjected to a reduction step prior to its use in the present process. This step is designed to insure a uniform and finely divided dispersion of the metallic component throughout the carrier material. Preferably, substantially pure and dry hydrogen (i.e., less than 20 vol. ppm. H O) is used as the reducing agent in this step. The reducing agent is contacted with the calcined catalyst at conditions including a temperature of about 800 F. to about 1000" F. selected to reduce substantially all of the platinum group component to the metallic state while maintaining substantially all of the germanium component in an oxidized state. This reduction step may be performed in situ as part of a start-up sequence if precautions are taken to predry the plant to a substantially water-free state and if substantially water-free hydrogen is used. In order to minimize the danger of reducing the germanium component during this step, the duration of this step is preferably less than two hours, and, more typically, about one hour.

The resulting reduced catalytic composite is, in accordance with the basic concept of the present invention, preferably maintained in a substantially sulfurfree state both during its preparation and thereafter during its use in the present process. It is, accordingly, a highly preferred practice to avoid presulfiding this bimetallic catalyst prior to its use in the present process. Even though any sulfur initially present on the catalyst would be removed during a first portion of the instant process, the preferred practice is to initially exclude all sources of sulfur from the reforming zone including sulfur contained in the catalyst.

According to the present invention, a hydrocarbon charge stock and hydrogen are contacted with a bimetallic catalyst of the type described above in a reforming zone which is maintained in a substantially sulfurfree state. This reforming zone may be one or more separate reactors with suitable heating means therebetween to compensate for the endothermic nature of the reactions that take place in each catalyst bed. The hydrocarbon feed stream that is charged to this reforming system will comprise hydrocarbon fractions containing naphthenes and paraffins that boil within the gasoline range. The preferred charge stocks are those consisting essentially of naphthenes and paraffins, although in many cases aromatics are also present. This preferred class includes straight run gasolines, natural gasolines, synthetic gasolines, and the like. On the other hand, it is frequently advantageous to charge thermally or catalytically cracked gasolines or higher boiling fractions thereof. Mixtures of straight run and cracked gasolines can also be used to advantage. The gasoline charge stock may be a full boiling gasoline having an initial boiling point of from about 50 F. to about 150 F. and an end boiling point within the range of from about 325 F. to about 425 F., or may be a selected fraction thereof which generally will be a higher boiling fraction commonly referred to as a heavy naphtha for example, a naphtha boiling in the range of C to 400 F. In some cases, it is also advantageous to charge pure hydrocarbons or mixture of hydrocarbons that have been extracted from hydrocarbon distillates for example, straight chain paraffms which are to be converted to aromatics.

An essential feature of the present invention is that the hydrocarbon charge stock is substantially free of sulfur. Quantitatively, use of the expression substantially free is intended to cover the situation where the total amount of sulfur contained in the charge stock in any form constitutes less than wt. ppm of same, and preferably less than 1 wt. ppm of same. Since in the ordinary operation of the conventional catalytic reforming process, wherein influent hydrogen is autogenously produced, the prime source for any sulfur entering the reforming zone is the charge stock, the above limitation is ordinarily sufficient to insure that the reforming zone containing the catalyst is maintained in the substantially sulfur-free state. More specifically, since hydrogen is a byproduct of the catalytic reforming process, ordinarily the input hydrogen stream required for the process is obtained by recycling a portion of the hydrogen rich stream recovered from the effluent withdrawn from the reforming zone. In this typical situation, this recycle hydrogen stream will ordinarily be substantially free of sulfur if the charge stock is maintained free of sulfur. If autogenous hydrogen is not utilized, then of course the concept of the present invention requires that the input hydrogen stream be maintained substantially sulfur-free; that is, less than 10 vol. ppm of H 8, and preferably less than 5 vol. ppm.

The only other possible sources of sulfur in this kind of process is sulfur that would be initially combined with the catalyst and/or with the plant hardware. As indicated herein before, a highly preferred feature of the type of bimetallic catalyst used in the instant process is that it be substantially sulfur-free; therefore, sulfur released from the catalyst is not usually a problem in the present process. Hardware sulfur is ordinarily not presentin a new plant; it only becomes a problem when the present process is to be implemented in a plant that has seen service with a sulfur-containing feed stream. In this latter case, the preferred practice of the present invention involves an initial pre-treatment of the sulfurcontaining plant in order to remove substantially all of the decomposable hardware sulfur thcreform. This can be easily accomplished by any of the techniques for stripping sulfur from hardware known to those in the art; for example, the circulation of the substantially sulfur-free hydrogen stream through the internals of the plant at a relatively high temperature of about 800 to about l200 F. until the H 8 content of the effluent gas stream drops to a relatively low level typically, less than 5 vol. ppm. in sum, the sulfur-free feature of the present invention requires that the total amount of sulfur entering the reforming zone containing the hereinbefore described bimetallic catalyst must be continuously maintained at a substantially low level; specifically, the

amount of sulfur must be held to a level equivalent to less than 10 wt. ppm, and preferably less than 1 wt. ppm, of the feed.

In the case where the sulfur content of the feed stream for the present process is greater than the amounts previously specified, it is, of course, necessary to treat the charge stock in order to remove the undesired sulfur contaminants therefrom. This is easily accomplished by using any one of the conventional catalytic pre-treatment methods such as hydrorefining, hydrotreating, hydrodesulfurization, and the like to remove substantially all sulfurous, nitrogenous and water-yielding contaminants from this feed stream. Ordi narily, this involves subjecting the sulfur-containing feed stream to contact with a suitable sulfur-resistant hydrorefining catalyst in the presence of hydrogen under conversion conditions selected to decompose sulfur contaminants contained therein and form hydrogen sulfide. The hydrorefining catalyst typically comprises one or more of the oxides or sulfides of the transition metals of groups VI and VIII of the Periodic Table. A particularly preferred hydrorefining catalyst comprises a combination of a metallic component from the iron group metals of group VIII and of a metallic component of the group VI transition metals combined with a suitable porous refractory support. Particularly good results have been obtained when the iron group component is cobalt and/or nickel and the group Vl transition metal is molybdenum or tungsten. The preferred support for this type of catalyst is a refractory inorganic oxide of the type previously mentioned. For example, good results are obtained with a hydrorefining catalyst comprising cobalt oxide and molybdenum oxide supported on a carrier material comprising alumina and silica. The conditions utilized in this hydrorefining step are ordinarily selected from the following ranges: a temperature of about 600 to about 950 F., a pressure of about 500 to about 5000 psig, a liquid hourly space velocity of about 1 to about 20 hr.', and a hydrogen circulation rate of about 500 to about 10,000 standard cubic feet of hydrogen per barrel of charge. After this hydrorefining step, the hydrogen sulfide, ammonia and water liberated therein, are then easily removed from the resulting purified charge stock by conventional means such as a suitable stripping operation. Specific hydrorefining conditions are selected from the ranges given above as a function of the amounts and kinds of the sulfur contaminants in the feed stream in order to produce a substantially sulfurfree charge stock which is then charged to the reforming process of the present invention.

In one mode of operation of the present invention it is applied to a reforming process which has been operated with a bimetallic catalyst of the type previously characterized and with a sulfur-containing charge stock. If the input hydrogen stream is obtained autogenously, the concept of the present invention would only require that the charge stock be pre-treated by one of the techniques previously discussed, to remove substantially all sulfurous, nitrogenous and water yielding contaminants therefrom. That is, in this case, only the charge stock need be pre-treated to bring its sulfur content down to the level previously specified in order to realize the benefits of the present invention. In this case, the residual sulfur in the reforming process will immediately start to fall because significant amounts of sulfur will be withdrawn from the system in the gaseous output stream, i.e., the excess recycle gas and the debutanizer overhead stream. After a while, the sulfur level in the process will decrease to the level where improved performance of the bimetallic catalyst will become evident. In the case where autogenous hydrogen is not utilized, then the concept of the present invention in this embodiment requires that both the input hydrogen stream and the charge stock be pro-treated to reduce the total amount of sulfur entering the reforming zone to the initial range given above. In either case, the improvement of the present invention is obtained by careful control over the total amount of sulfur continuously entering the reforming zone and it is this parameter that is the crucial parameter here.

It is generally preferred to utilize this bimetallic catalyst in a reaction environment in which the amount of water is held to carefully controlled levels. Essential to the achievement of this condition in the reforming zone is the control of the water level present in the charge stock and the hydrogen stream which are charged to the zone. Best results are ordinarily obtained when the total amount of water entering the zone from any source is held to a level in the range corresponding to about to about 50 wt. ppm, expressed as weight of equivalent water in the charge stock. In general, when the amount of water entering this zone is greater than desired, a significant reduction can be accomplished by careful control of the water present in the charge stock and in the hydrogen stream; the charge stock and the hydrogen stream can be dried by using any suitable drying means known to the art such as a conventional solid adsorbent having a high selectivity for water; for instance, sodium or calcium crystalline aluminosilicates, silica gel, activated alumina, molecular sieves, anhydrous calcium sulfate, high surface area sodium, and the like adsorbents. Similarly, the water content of the charge stock may be adjusted by suitable stripping operations in a fractionation column or like device. And, in some cases, a combination of adsorbent drying and distillation drying may be used advantageously to effect almost complete removal of water from the charge stock. In the case where the total amount of water entering the reforming zone is below the desired range, the required amount of water is achieved by introducing into the reforming zone a suitable water additive such as water or an oxygen-containing substance that is reducible to water at reforming conditions. Typical oxygen-containing compounds that can be used are the alcohols, aldehydes, ketones and the like.

The reforming zone is operated under conditions selected to produce a high octane C reformate. The pressure utilized is preferably selected in the range of about 50 psig to about 350 psig. In fact, it is a singular advantage of the present invention that it allows stable operation at lower pressures than have heretofore been successfully utilized in so-called continuous" reforming systems (i.e., reforming for periods of about I5 to about 200 or more barrels of charge per pound of catalyst without regeneration). In other words, the present invention allows the operation of a continuous reforming system to be conducted at lower pressure (i.e., 50 to 350 psig) for about the same or better catalyst life before regeneration as has been heretofore realized with conventional catalysts at higher pressures (i.e., 400 to 600 psig).

Similarly, the temperature required for reforming is generally lower than that required for a similar reforming operation using a high quality catalyst of the prior art. This significant and desirable feature of the present invention is a consequence of the selectivity of the bimetallic catalyst of the present invention for octaneupgrading reactions that are preferably induced in a typical reforming operation. Hence, the present invention requires a temperature in the range of from about 800 F. to about I F. and preferably about 900 F. to about l050 F. As is well known to those skilled in the continuous reforming art, the initial selection of the temperature within this broad range is made primarily as a function of the desired octane of the product reformate considering the characteristics of the charge stock and of the catalyst. Ordinarily, the temperature then is thereafter slowly increased during the run to compensate for the inevitable deactivation that occurs to provide a constant octane product. Therefore, it is a feature of the present invention that the rate at which the temperature is increased in order to maintain a constant octane product is substantially lower for the process of the present invention than for a reforming process which is operated in exactly the same manner as the process of the present invention except for the exclusion of sulfur therefrom. Moreover, for the process of the present invention, the C yield loss for a given temperature increase is substantially lower than for a reforming process of this type operated with sulfur inclusion. In addition, hydrogen production is substantially higher with the present process.

The reforming process of the present invention also typically utilizes sufficient hydrogen to provide an amount of about 2 to about 20 moles of hydrogen per mole of hydrocarbon entering the reforming zone, with excellent results being obtained when about 5 to about l0 moles of hydrogen are used per mole of hydrocarbon. Likewise, the liquid hourly space velocity (Ll-ISV) used is selected from the range of about 0.1 to about I0 hr., with a value in the range of about 1 to about 5 hr. being preferred. In fact, it is a feature of the present invention that for the same severity level, it allows operations to be conducted at higher LHSV than normally can be stably achieved in a continuous 'reforming process with a high quality reforming catalyst of the prior art. This last feature is of immense economic significance because it allows a continuous reforming process to operate at the same throughput level with less catalyst inventory than that heretofore used with conventional reforming catalysts at no sacrifice in catalyst life before regeneration.

It is intended to cover by the following claims, all changes and modifications of the above disclosure of the present invention that would be self-evident to a man of ordinary skill in the catalytic reforming art.

I claim as my invention:

. l. A process for catalytically reforming a substantially sulfur-free gasoline fraction, which comprises contacting, at reforming conditions, the gasoline fraction and a substantially sulfur-free hydrogen stream with a substantially sulfur-free catalyst comprising a combination of a platinum group component, a germanium component and a halogen component with a porous carrier material, in which catalyst substantially all of the platinum group component is present as the elemental metal and substantially all of the germanium component is present in an oxidation state above that of the elemental metal and in which catalyst said components are present in amounts sufficient to result in the catalyst containing, on an elemental basis, about 0.01 to about 2 wt. percent of the platinum group metal, about 0.01 to about 5 wt. percent germanium and about 0.5 to about 3.5 wt. percent halogen.

2. A process as defined in claim 1 wherein the platinum group component of the catalyst is platinum metal. 1

3. A process as defined in claim 1 wherein the germanium component of the catalyst is germanium oxide.

4. A process as defined in claim 1 wherein the halogen component of the catalyst is chlorine or a compound of chlorine.

5. A process as defined in claim 1 wherein the porous carrier material is a refractory inorganic oxide.

6. A process as defined in claim 5 wherein said refractory inorganic oxide is gammaor eta-alumina.

7. A process as defined in claim 1 wherein the hydrogen stream is obtained autogenously and the gasoline fraction contains less than about wt. ppm of sulfur.

8. A process as defined in claim 1 wherein the total amount of sulfur entering the reforming zone is continuously maintained at a value corresponding to less than about 10 wt. ppm of the gasoline fraction.

9. A process as defined in claim 1 wherein the total amount of water entering the reforming process corresponds to about 10 to about 50 wt. ppm of the gasoline fraction. I

10.1n the process for catalytically reforming a sulfurcontaining gasoline charge stock wherein the charge stock and autogenous hydrogen are contacted, at reforming conditions, with a catalyst comprising a combination of a platinum group component, a germanium component and a halogen component with a porous carrier material, wherein substantially all of said platinum group component is present in the catalyst as the elemental metal and substantially all of said germanium component is present in the catalyst in an oxidation state above that of the elemental metal, and wherein said components are present in the catalyst in amounts sufficient to result in the catalyst containing, on an elemental basis, about 0.01 to 2 wt. percent platinum group metal, about 0.l to about 5 wt. percent germanium and about 0.5 to about 3.5 wt. percent halogen, the improvement which comprises pretreating the gasoline charge stock to remove substantially all sulfurous, nitrogenous and water-yielding contaminants therefrom. 

2. A process as defined in claim 1 wherein the platinum group component of the catalyst is platinum metal.
 3. A process as defined in claim 1 wherein the germanium component of the catalyst is germanium oxide.
 4. A process as defined in claim 1 wherein the halogen component of the catalyst is chlorine or a compound of chlorine.
 5. A process as defined in claim 1 wherein the porous carrier material is a refractory inorganic oxide.
 6. A process as defined in claim 5 wherein said refractory inorganic oxide is gamma- or eta-alumina.
 7. A process as defined in claim 1 wherein the hydrogen stream is obtained autogenously and the gasoline fraction contains less than about 10 wt. ppm of sulfur.
 8. A process as defined in claim 1 wherein the total amount of sulfur entering the reforming zone is continuously maintained at a value corresponding to less than about 10 wt. ppm of the gasoline fraction.
 9. A process as defined in claim 1 wherein the total amount of water entering the reforming process corresponds to about 10 to about 50 wt. ppm of the gasoline fraction.
 10. In the process for catalytically reforming a sulfur-containing gasoline charge stock wherein the charge stock and autogenous hydrogen are contacted, at reforming conditions, with a catalyst comprising a combination of a platinum group component, a germanium component and a halogen component with a porous carrier material, wherein substantially all of said platinum group component is present in the catalyst as the elemental metal and substantially all of said germanium component is present in the catalyst in an oxidation state above that of the elemental metal, and wherein said components are present in the catalyst in amounts sufficient to result in the catalyst containing, on an elemental basis, about 0.01 to 2 wt. percent platinum group metal, about 0.1 to about 5 wt. percent germanium and about 0.5 to about 3.5 wt. percent halogen, the improvement which comprises pretreating the gasoline charge stock to remove substantially all sulfurous, nitrogenous and water-yielding contaminants therefrom. 